drm/i915/guc: fix GuC loading/submission check

The last stage of the GuC loader also sanitises the GuC submission
settings, so should be called unconditionally (even on platforms
without a GuC) to ensure consistent settings; in particular, this
prevents any attempt to use GuC submission on GuCless platforms!

Also fix error path handling and clarify DRM_INFO fallback message.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -4930,11 +4930,9 @@ i915_gem_init_hw(struct drm_device *dev)
 	intel_mocs_init_l3cc_table(dev);
 
 	/* We can't enable contexts until all firmware is loaded */
-	if (HAS_GUC(dev)) {
-		ret = intel_guc_setup(dev);
-		if (ret)
-			goto out;
-	}
+	ret = intel_guc_setup(dev);
+	if (ret)
+		goto out;
 
 	/*
 	 * Increment the next seqno by 0x100 so we have a visible break

drivers/gpu/drm/i915/intel_guc_loader.c

@@ -425,9 +425,13 @@ int intel_guc_setup(struct drm_device *dev)
 	if (!i915.enable_guc_loading) {
 		err = 0;
 		goto fail;
-	} else if (fw_path == NULL || *fw_path == '\0') {
-		if (*fw_path == '\0')
-			DRM_INFO("No GuC firmware known for this platform\n");
+	} else if (fw_path == NULL) {
+		/* Device is known to have no uCode (e.g. no GuC) */
+		err = -ENXIO;
+		goto fail;
+	} else if (*fw_path == '\0') {
+		/* Device has a GuC but we don't know what f/w to load? */
+		DRM_INFO("No GuC firmware known for this platform\n");
 		err = -ENODEV;
 		goto fail;
 	}
@@ -535,7 +539,7 @@ int intel_guc_setup(struct drm_device *dev)
 		if (fw_path == NULL)
 			DRM_INFO("GuC submission without firmware not supported\n");
 		if (ret == 0)
-			DRM_INFO("Falling back to execlist mode\n");
+			DRM_INFO("Falling back from GuC submission to execlist mode\n");
 		else
 			DRM_ERROR("GuC init failed: %d\n", ret);
 	}